Method of preventing corrosion in oil wells



Patented Aug. 23, 1932 UNITED STATES PATENT OFFICE JOHN CHARLES WALKER,-OF TALLANT, OKLAHOMA, ASSIGNOR 'I'O OIL AND REFINING GOMPANY,-OF DOV ER,DELAWARE, A CORPORATION OF DELAWARE mnrnon or ranvnnmmo connosloiv m on.WELLS No Drawing.

part.

It is the particular object of the present invention to provide aprocess for treating oil well liquids whereby the serious losses ofmaterial and time which are normally caused by the corrosive attacks bysuch liquids on casings, pumps, and other metal parts installed in thewell are prevented or avoided.

Among the compounds present in oil well liquids which have been found tobe responsible for the corrosion of metal parts in contact with suchliquids are acidic salts such as ferrous and ferric chlorides andsulphates, and magnesium chlorides and sulphates. These acidic saltshydrolize to some extent to form the metal oxide or hydroxide andmineral acid. Any oxygen present in the well liquids causes acceleratedcorrosion of metal parts in contacttherewith. Sometimes very corrosivewell waters give an alkaline reaction to methyl orange indicator,showing the absence .in such liquids of free strong mineral acids. Mostof these corrosion promoting compounds are acidic in char-- acter andmany of them are very active in destroying iron and steel parts.

The present invention contemplates the prevention of corrosion of metalparts in contact with oil well liquids (particularly the brines ornatural waters produced with the oil) containing one or more of suchcom-,

. pounds. pounds, preferably in alkaline solution, are

To accomplish this, chromium com introduced into the oil well in such amanner as to be brought into intimate contact with the liquids in thewell. These compounds act to neutralize acidic or corrosive componentsof the well liquids and to render the.

Application filed July 19, 1 928. Serial No. 294,067.

metal parts passive or resistant to corrosive attack by the wellliquids.

The invention also contemplates the prevention of scale formation onmetal arts in oil wells by holding any precipitate matter which normallyforms the scalein a form such that it will be carried out of the wellwith the water and oil pumped from the well.

If oil well waters or brines come in contact with carbonic acid oroxygen, or contain either one and come incontact with the other, .orcontain .both carbonic acid and oxygen, iron oxide (hydrated) is formedupon contact of such brine with metal parts in the well; such oxidebeing deposited on the iron parts of the well as scale (rust). A

further source of troublesome scale is strontium chloride or othersoluble strontium salt which is contained in the top waters of wells inmany localities. Upon admixture of strontium containing top waters withbottom waters containing sodium or calcium sulfate in solution, forexamle, strontium sulfate is formed. Normally t e strontium sulfate isformed slowly because of the high concentration of the chloride ions,and accordingly deposits as a very hard compact scale. While strontiumsulfate does not itself have any extensive corrosive efl'ect, itsdeposition as a hard scale causes serious mechanical troubles. Ingeneral the scales encountered or formed during oil well operation, afew of which are referred to above, promote rather than inhibit thecorrosion of metal parts in contact with the oil well liquids, as wellas interfering with the proper operation of the pumping apparatus whichmay be installed at the bottom of the well.

It has been found that caustic soda has a very strong neutralizingeffect on the acidic components of oil well brines, but-that its use isgenerally disadvantageous for the reason that it reacts .quickly andapparently selectively with calcium and magnesium salts contained in thebrines, thus rapidly depleting the neutralizing strength of the. causticand forming undesirable precipitates of calcium-and magnesium waterinsoluble salts. Accordingly if sodium hydroxide is used alone as acorrosion inhibiting treating agent for the well liquids, it usuallytakes an undesirably large amount of the caust1c soda to accomplish thedesired corrosion inhibiting.

. results, and furthermore undesirable preci itates are formed which addto the difliculties of pumping or otherwise operating the well.

ably formed by mixing salts of chromous or chromic acid with a slightexcess of caustic soda. The amount of excess of caustic soda employed inmaking up the sodlum chromate solution is governed by the composition ofthe well liquids to be treated, and is normally so adjusted that thewell liquids are rendered substantially neutral or preferably slightlyalkaline by the treatment wlthout, however, carrying the neutralizationfar enough to precipitate appreciable quantities of calcium or magnesiumcarbonates 1n cases where the well liquids contain such alkaline earthsin the form of bicarbonates. V

In place of sodium chroma-te other salts of chromous or chromic acid mayin many cases be used to advantage, such for example as other alkalimetal or ammonium chromates and dichromates. In employing an excess ofalkali as above described, any d1- chromates used will be converted tochromates. If for any reason it is not desired to use an alkali solutionof the treating agent, the dichromates may in general be used toadvantage. In treating certain types of well liquids oil-solublechromium compounds such as chromium resinate are in some casesadvantageously employed. The invention therefore contemplates theaddition to the' well liquids of chromium either in the form of an acidradical as in the chromate or in the form of a basic metal ion asinchromium resinate.

The chromium as it is added to the oil well liquids, for example in theform ofa caustic solution of sodium chromate, has been found to be veryeffective for reducing the corrosive action of, the well liquids (aswell as for preventing or retarding rust scale formation). The sodiumchromate solution reacts slowly with any calcium and magnesium salts inthe well liquids. No insoluble calcium or magnesium salts are usuallyformed for the reason that the sodium chromate is used in such smallquantities that the solubility of the alkaline earth chromates in thelarge excess of brine is not exceeded. The caustic sodium chromatesolution normally has sufiiciently active neutralizing properties topacify the acidic or corrosive properties of the oil well brines and torender inactive any oxygen present in the well liquids.

The sodium chromate solution acts to keep the metal surfaces in contactwith the well liquids clean and its use therefore materially aids thepumping of the well in that the pump iston and packing operate much moreef- Eciently in the working barrel, and the friction losses are held ata minimum. The action in turn aids in lessening the amount of powerwhich is used in pumping and in lessening the strain on the pumping rodsand associated parts.

Treatment of the well liquids with an alkaline solution of sodiumchromate prevents the formation of rust or hydrated ferric oxide scaleon the metal parts. By adding to the treating agent a small amount of anorganic or inorganic colloid or colloidal forming material such astannic acid, glue or sodium silicate, the treating agent may be madeeffective for inhibiting the formation of adherent hardscales ofstrontium sulfate and the like. Such colloidal or gelatinous componentof the treating agent causes the scale forming materials to remain insuspension in the-well liquids until they are carried to the surface bythe action of the well pump. Potassium and sodium dichromates aresometimes used to advantage, either alone or in alkaline solution. Ingeneral the chromate or chromium compound in alkaline solution isparticularly effective for treating well liquids the corrosive action ofwhich is chiefly due to mineral acids or acid salts with or without thepresence of oxygen or carbon dioxide or both oxygen and carbon dioxidein the brine. In cases where the corrosive action of well liquidsisessentially of the oxidation type and there is substantially no freeacid present in the brine, the di-chromate, chromate, chromous acid, orchromic acid may generally be employed alone to advantage because suchreagents render the iron parts in contact with the well liquids passivewithout causing precipitation of insoluble calcium or magnesiumcarbonate.

When treating the liquids in the well ac cording to the presentinvention, it has been found that it is necessary for best results andfor the best protection of all the metal parts of or in the well thatthe corrosion inhibiting compound'difluses rapidly through the wellliquids on being added thereto. This result is accomplished according tothe present invention by making up the treating agent in a brine or saltwater solution having a specific gravity substantially the same as thespecific gravity of the water in the well to be treated. In making upthe treating agent latter case a calculated excess of caustic or otherneutralizingcompound is added to compensate for the calcium saltsprecipitated from the brine component of the solution.

The chemical or neutralizing agent may be added to the well in variousways. One satisfactory schedule of operation is to introduce 50% or moreof the reagent solution between the casing and the pump delivery pipe asrapidly as possible just after the pump is started. The remainder of thereagent is added in the same way but about fifteen minutes before thewell is pumped off. However, when the well pumps continuously and withsuch metal parts.

2. A method of preventing corrosion of metal parts in contact with oilwell liquids,

comprising adding to the well liquids a solu- ,tion of a chromiumcompound in amounts sufficient to inhibit corrosion of the oxidationtype Without causing precipitation of insoluble alkaline earth salts.

3. A method of preventing corrosion of metal parts in contact with oilwell liquids comprising treating such liquors prior to removal thereoffrom the well with a caustic solution of sodium chromate in amountssufficient to inhibit corrosion of the oxidation type without causingsubstantial'precipitation of insoluble alkaline earth salts.

4. A method of preventing corrosion of metal parts by oil well liquidscomprising mixing with the Well liquids a solution of a chromium salthaving a specific gravity substantially equal to that of the well water.

5. A method of preventing corrosion of metal parts in contact with oilwell liquids comprlsing mixing with the well liquids an' aqueous.solution of sodium chromate having substantially the same specificgravity as the well water.

6. A method of preventing corrosion of metal parts in contact withliquids from oil wells comprising mixing with said liquids an alkalinesolution of an oil soluble chromium compound.

In testimony whereof I atfix my signature.

JOHN CHARLES WALKER.

